1. Field of the Invention
The present invention relates to disk drive systems and, more specifically, to an apparatus for determining if space is available in a WRITE data buffer for a WRITE operation and if the sectors are available for transfer in a READ data buffer for a READ operation.
2. Description of the Related Art
In some present disk drive systems a READ buffer and a WRITE buffer are used to buffer data being transferred between the host and the disk. These buffers may be separate RAMs or can be a single RAM that is partitioned into the two separate buffers. The use of the READ and WRITE buffers allows the disk drive system to receive data from the host for storage in the WRITE buffer while, at the same time, retrieving data from the disk for storage in the READ buffer, or for transferring data from the WRITE buffer to the disk while, at the same time, transferring data from READ buffer 1 to the host.
In disk drive systems that use READ and WRITE buffers it becomes necessary to monitor the amount of data available in the READ buffer for a requested READ operation and the amount of space available in the WRITE buffer for a requested WRITE operation. A sector of data, 512 bytes of data, is the basic unit of transfer of data in many disk drive systems. Since in a READ and WRITE operation more than one sector may be transferred, the host will provide the disk drive system with the number of sectors to be transferred. Data is stored in the READ and WRITE buffers as sectors where each buffer can store up to 2,000 to 3,000 sectors.
The disk drive system has a microprocessor, under program control, which controls the overall operation of the disk drive system. One function performed by the microprocessor is to determine if a requested WRITE operation can be performed, that is, the availability of space within the WRITE buffer for a requested WRITE operation. If a requested READ operation can be performed, that is, the availability of sectors in the READ buffer for a requested READ operation and if the READ or WRITE operation can be performed, to generate an OK TO TRANSFER signal indicating the same in the disk drive system. The processing overhead on the microprocessor for performing this function can become large enough to degrade the overall disk drive system's performance and efficiency characteristics.